The present invention generally relates to drying liquid printing substances such as inks, coatings and the like applied to sheet material in a printing press by heating the sheet material as it is moving through the printing press, and more particularly to a safety system for use with printing presses having infrared dryer systems operable at high temperatures for heating and drying the passing sheet material.
One of the major concerns associated with the use of printing systems having infrared dryers is that such infrared dryers have high operating temperatures, which can be up to 800-1000xc2x0 F. If the boards, sheets or other printed substrate material become jammed in the area of the infrared dryer, the heat produced by the infrared dryer can ignite the substrate material and not only cause damage to the printing equipment, but jeopardize the safety of personnel in the surrounding area.
Heretofore, efforts to detect sheet jams and overheating often have required separate monitoring systems which are not wholly effective and which can result in unnecessary shut-down of the printing press. For example, temperature-sensing systems do not necessarily sense a sheet jam prior to an overheating condition, which can result in potential damage to the printing press. Systems that detect sheet travel interruption, i.e., jam, may not sense potential fire conditions and can result in unnecessary shutdown of the press. Prior temperature sensing systems also can be unreliable by detecting only the temperature in the vicinity of the passing sheet material, and not the temperature of the sheet material itself.
It is an object of the present invention to provide a printing press with one or more infrared substrate dryer units having a safety system, which more reliably guards against overheating and fire hazards associated with the high operating temperatures of infrared dryers.
Another object is to provide a printing press as characterized above with a temperature-responsive safety system for sensing the interruption of sheet flow through the printing press and fire hazards associated therewith.
A further object is to provide a printing press having infrared dryer units and a unitary safety system for both sensing the interruption in sheet flow and associated fire hazards.
Still another object is to provide an infrared dryer safety system for printing presses that is relatively simple in construction and operation and which lends itself to easy field retrofitting. More particularly, it is an object to provide such an infrared dryer safety system which utilizes a single sensor for detecting both sheet jams and potential fire hazards caused by the interruption of the flow of sheet material.
Yet another object is to provide an infrared dryer safety system that is more reliable by directly sensing the temperature of passing sheet material.
Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings, in which: